1. Field of the Invention
The present invention relates to a valve timing adjusting apparatus for changing opening/closing timing (referred to hereafter simply as valve timing) of at least one of an intake valve and an exhaust valve of an internal combustion engine (referred to hereafter simply as an engine).
2. Description of Related Art
A vane type valve timing adjusting apparatus for controlling the valve timing of at least one of an intake valve and an exhaust valve is well known. Typically, the apparatus operates by driving a camshaft through a timing pulley or a chain sprocket rotating in synchronization with a crank shaft of the engine in accordance with a difference in phase between the camshaft and the timing pulley or the chain sprocket. Such an apparatus is disclosed in Japanese Patent Laid-open No. Hei 1-92504.
In the valve timing adjusting apparatus disclosed in Japanese Patent Laid-open No. Hei 1-92504, a hole is provided on an internal rotor which is a rotary body on the camshaft side rotating along with a vane. A knock pin that can be fit in the hole is provided on the timing pulley, a rotary body on the crank shaft side. When the camshaft comes to an optimum position or an optimum angle with respect to the timing pulley, the knock pin is fit in the hole to restrain relative rotation between the two rotary bodies. As a result, when the camshaft is positioned at the most lagging angular position or the most leading angular position with respect to the timing pulley, it is possible to prevent sound from being generated due to an impact of the vane on the timing pulley even if a positive or negative change in torque is applied to the camshaft according to the driving of either an intake valve or an exhaust valve.
In order to change the phase of the camshaft relative to the timing pulley from the state where the knock pin is fit in the hole, a hydraulic path needs to be changed to pull out the knock pin from the hole so that the timing pulley can rotate relative to camshaft.
However, a vane-type valve timing adjusting apparatus such as that described above typically adopts a technique that causes the knock pin to be pulled out from the hole by an oil pressure to drive the vane to the leading angle side at the same time as the camshaft. The camshaft, which is located at a most lagging angular position with respect to the timing pulley, is then also rotated forward toward the leading angleside. Before the knock pin is pulled out from the hole, the internal rotor may start to rotate in some cases depending upon the timing of oil application to the vane and the knock pin. As a result, a force generated by the rotation of the internal rotor may be applied to the knock pin, causing a damage to the knock pin and members around the knock pin.
In addition, the knock pin is pulled out from the hole and the camshaft is rotated to the leading or lagging angle side after the hydraulic path is changed. As a result, it is often difficult to improve the response characteristic of phase control of the camshaft with respect to the timing pulley.